A process for cooling hot gas/solids suspensions

ABSTRACT

A hot gas/solids suspension, of the kind formed during the reaction between gaseous metal halides and gases containing oxygen, is cooled by introduction of cold gas either radially or annularly. The suspension, flowing through a pipe at about 10 to 100 meters per minute, passes into a cylindrical chamber where its direction of flow is changed abruptly to produce turbulence and its flow rate is reduced to less than one-half its previous level. The direction of flow of the suspension is then abruptly changed again, the chamber discharging into a pipe so that the flow rate is increased. Means are provided to scrape away any solids which may deposit in the chamber. In this manner the cooling is controlled which, in turn, controls the form of the solids.

United States Patent 191 Zirngibl et al. 1 5] Apr. 17, 1973 [s41 PROCESSFOR COOLING HOT 3,406,012 10/1968 1am ..23/202 v GAS/SOLIDS SUSPENSIONS3,498,757 3/1970 3,363,980 1 1968 [75] Invenmrs: Hm Dulsburg; Klemens3,214,284 10 1965 Wilson ..23 202 v Jaschinsld, Krefeld-Uerdingen; KarlBrandle, Krefeld; Walter Weidmann, Duisburg-Muendelheim, all of GermanyBayer Aktiengeselbchaft, Leverkusen, Germany Filed: Jan. 15, 1971 Appl.No.: 106,758

Foreign Application Priority Date Feb. 4, 1970 Germany .Q. ..P 20 05 011.7

US. Cl ..55/72 Int. Cl. ..Bold 57/00 Field of Search ..55/71, 72; 23/87T,

References Cited UNITEDSTATES PATENTS Belknap et al ..23/202 V PrimaryExaminer-Charles N. Hart Attorney-Burgess, Dinklage & Sprung [57]ABSTRACT A hot gas/solids suspension, of the kind formed during thereaction between gaseous metal halides and gases containing oxygen, iscooled by introduction of cold gas either radially or annularly. Thesuspension, flowing through a pipe at about 10 to 100 meters per minute,passes into a cylindrical chamber where its direction of flow is changedabruptly to produce turbulence and its flow rate is reduced to less thanonehalf its previous level. The direction of flow of the suspension isthen abruptly changed again, the chamber discharging into a pipe so thatthe flow rate is increased. Means are provided to scrape away an solidswhich may deposit in the chamber.

In this manner the cooling is controlled which, in turn, controls theform of the solids.

9 Claims, 3 Drawing Figures PAIENTEB I 1875 727, 378

sum 1 0F 2 FIG. 2

INVENTORS: HANS ZIRNGIBL, KLEMENS JASCHINSKI, KARL BRANDLE, WALTERWEIDMANN.

PATENTE[1VAPR17I373 3. 727, 378

sum 2 [IF 2 FIG 3 INVENTORS: HANS ZIRNGIBL, KLEMENS JASCHINSKI, KARLBRANDLE, WALTER WEIDMANN.

il- 7 A y PROCESS FOR COOLING HOT GAS/SOLIDS SUSPENSIONS metal oxides,for example TiO A1 and SiO,, which I can be used aspigments. Whengradually cooled, these hot oxides show a marked tendency to adhere tothe walls and form coatings. This can continue to such an extent thatthe pipe lines become increasingly narrower until finally they arecompletely obstructed and production has to be suspended.

in addition, in the production of oxidic pigments such as TiO forexample, the properties of the pigments are influenced to a large extentby the cooling program. If TiO, particles produced in this way remaintoo long in the high temperature zone, the particles undergo undesired,irregular growth into coarse material whose optical properties, forexample brightening power, have deteriorated to a considerable extent.The increase in the size of the pigment particles is accompanied by awidening of the particle size distribution which also has a negativeinfluence on the pigment properties. Accordingly, the product stream,after leaving the reactor at temperatures in excess of 1000C, has to becooled asquickly as possible to temperatures of 800C or lower. 1

If by contrast the residence time in the high tempera All the processesreferred to above have certain disadvantages. Thus, the cold gas ispiped without any special precautionary measures. The mixing operationis not controlled in any way. Poor admixture is accompanied by theformation of strands, resulting in delayed or nonuniform temperatureequalization. In some cases, uncontrolled flow cycles can result inre-admixture movements which can react back to the flame. Similarly,pressure can be subjected to periodic fluctuations. The result of thesevarious phenomena are the aforementioned negative effects upon thepigment such as, for example, wide particle size distribution or poorhabit development of the particles with numerous faults as a result ofexcessive chilling.

It is accordingly an object of the invention to provide a coolingprocess and apparatus which are substantially trouble-free and whichpermit close control over the U.S. Pat. Specification No. 2,394,633relates to a process in which the product gas stream is quickly cooledto a temperature of from 450 to 800C without any special precautionarymeasures, and the oxidic material subsequently deposited.

According to U.S. Pat. Specification No. 2,488,439,

the product gas stream in the production of TiO,

(chlorine with smallquantities of oxygen) is cooled very quickly to 600Cby recycling cold end gas.

According to U.S. Pat. Specification No. 2,508,272, which also relatesto the production of 110,, the product is similarly cooled as quickly aspossible with cold recycle gas. a

Finally, reference is made to the process disclosed in U.S. Pat.Specification No. 2,833,627 in which the TiO, suspension leaving thefurnace at a temperature of about 1300C is passed through a water-cooledaluminum pipe following the addition of cooled, dust-free recycled gas,and is cooled in this tube to from about 1000C to 100C.

form of the solids ultimately recovered.

These and other objects and advantages are realized in accordance withthe present invention.

A process for cooling gas/solids suspensions of the kind formed duringthe reaction of a metal halide with a gas containing oxygen in the gasphase by mixing the gas/solids suspension with cold gas wherein cold gasis delivered to the reaction gas through nozzles or annular gaps, theresulting gas/solids stream is delivered with a change in direction toreduce the rate of flow into a widening chamber on whose walls thedevelopment of deposits is mechanically prevented, after which thegas/solids stream is delivered with another change in direction througha pipe of narrowed cross-section to the gas/solids separation stage. r I

The object of the present invention is to control the cooling operation.It should be neither too quick nor too slow, strand formation should beavoided and the temperature should be equalized over a predetermineddistance. Surprisingly, it has been found that the problem can be solvedif, following; introduction of the cold gas, the product stream is madeto undergo an abrupt change in direction and the rate of flow of thesuspension simultaneously reduced to a considerable extent. The productstream is preferably deflected through approximately into a vastly widerchamber. The turbulence generated through this change in direction andthe considerable decrease in the rate of flow together produce completetemperature equalization. The product stream of uniform temperature thenundergoes a second change in direction, again preferably through about90, and is finally delivered to an arrangement in which the solidscomponent is separated from the gas. Surprisingly, the second change indirection and the drastic change in the rate of flow togetheradditionally produce a coagulating effect. The at least partlycoagulated product can subsequently be deposited with much greatereffect.

one twentieth of the original flow rate. In the deflection chamber, thetemperature of the gas/solids suspension is in the range from about 700to 1000C and preferably in the range from about 750 to 850C. At theoutlet end of the deflection zone, the temperature should reach or bebelow about 800C. A temperature range of from about 500 to 800C ispreferred. The gas/solids stream is then subjected to another change indirection and delivered through a pipe of narrowed crosssection (inorder to increase the rate of flow, preferably to about 30 to 200percent of the level prevailing at the outlet end of the reactor) to thegas/solids separation arrangement.

Gases that are .inert to the reaction may be used as the cold gas. Inthe production of oxides from the corresponding halides, it is ofadvantage to use the cold, dust-free recycle gas. A gas of this kind canconsist, for example, of chlorine, CO, and traces of oxygen.

According to the invention, the cold gas is delivered to the hot solidssuspension by introducing the cold gas into a water-cooled arrangementwhich comprises an annular duct and nozzles extending from this annularduct inside, preferably radially arranged, andin which, after it hasbeen distributed in the aforementioned annular duct, the cold gas flowsinwards through the nozzles and penetrates into the reaction product inthe form of jets.

The cooling operation can be additionally influenced by inclining thecold gas nozzles. Where the nozzles are horizontally arranged, i.e.,transversely of the product gas stream, the temperature of the productstream is rapidly lowered, although complete temperature equalizationonly takes place afterwards in the widened chamber after the change ofdirection. If by contrast the cold gas is guided parallel to the productstream (through nozzles directed parallel to the wall or through anannular gap), cooling only takes place in the peripheral zone. In thiscase, complete temperature equalization only takes place after thechange of direction or deflection. This makes it possible to shorten ofextend the high temperature zone and hence to influence the particlesize and to some extent also the particle size distribution by suitablyselecting the angle of inclination of the cold gas nozzles.

As a result of the sharp change in direction and the accompanyingturbulence, solids are inevitably deposited upon the walls of thedeflection chamber where they settle. Accordingly, there is provided inthe widening chamber a rotatable frame which is provided with a coolingsystem and which rotates slowly and prevents excessive deposits orstrips off any deposits that may have accumulated. This frame rotatesvery slowly at a peripheral speed of from about 0.01 to 0.7 meter persecond. I

The rotatable frame also prevents relatively large quantities of productfrom remaining too long in the high temperature zone in the form ofdeposits, as a result of which they would be deprived in time of theirfavorable optical properties.

Because it is water cooled, this rotatable frame can be made from metalswhich are resistant to the gas. In the production of TiO,, aluminum ornickel is recommended. If the solids product emanating from the reactionis extremely hard, such as rutile for example, the aluminum will in timebe eroded at those places where it scrapes off the product. Tocounteract this, it is advisable to provide hard materials at theendangered areas. For example, hardened metal strips or strips of aresistant ceramic material such as aluminum oxide or steatite forexample can be applied.

The process according to the invention and the apparatus in which it iscarried out are described in the following with reference to FIGS. 1 to3 of the accompanying drawings where in:

FIG. 1 is a schematic, longitudinal section through the apparatus;

FIG. 2 is a section on line 22 of FIG. 1; and

FIG. 3 shows another embodiment differing from FIG. 1 in the delivery ofthe cooling gas.

Referring now more particularly to the drawings, in FIG. 1, the hotgas/solids suspension leaves the actual reactor in which the solidscomponent is formed at l. A plate 2, preferably made of metal, which isprovided with'a water cooling system 3 and which is used to deliver thecold gas is inserted into the reactor. The cold gas is introducedthrough the socket 4, distributed over the periphery in the annular duct5 and introduced radially through the nozzles 6 into the product stream.There then follows an apparatus section made of watercooled metal, whichconsists of a large cylindrical chamber 7 which is fitted with arotatable, watercooled frame 8 and which has one cylindrical inlet 9 andone cylindrical outlet 10 for the gas/solids suspension. The inlets andoutlets are arranged opposite one another (see FIG.2 on the periphery ofthe large chamber and extend in opposite directions. The product isfurther cooled and deposited after passing through the outlet 10. v

The embodiment of FIG. 3 differs in that the cooling gas is dischargedthrough an annular gap 6' so that it moves parallel to the hot gas.

The process according to the invention is suitable for cooling anygas/solids suspensions of the kind formed in gas-phase reactions. Aboveall, it can be used with particular advantage in the production ofpigments by the gas-phase decompositon of metal halides, for example thechlorides of Ti, Si, Zr, Cr, Al, Fe or Zn, with gases containing oxygenat elevated temperatures.

The invention is illustrated by the following Example which describesthe production of finely divided pigment TiO,.

EXAMPLE The apparatus used for the process corresponds to thatillustrated in FIG. 1. The outlet from the reactor 1 had a diameter ofmm. The dimensons of the large, widened chamber in which the changes indirection take place were as follows:

The internal diameter of the chamber 1 was 679 mm, and the internalheight 350 mm. The'rotatable frame had an outer diameter of 630 mm. Theframe rotates at a speed of 5 rpm corresponding to a peripheral speed ofapproximately 0.2 meter per second.

TiCI, vapor at a temperature of 500C to which aluminium chloride vapourhad been added was reacted with a hot gas stream of oxygen and CO, inthe reactor.

On completion of the reaction, the following mixture issued from thereactor at 1: 244 Nmlh reaction gas with 200 kg/h TiO,. The gascontained 77.0 percent by volume of chlorine, 12.6 percent by volume ofCO, and 10.4 percent by volume of 0,.

The temperature stabilized at 760C. The cooled reaction mixture left thearrangement at whose diameter was 80 mm, after which it was delivered toanother cooling and wet-disposition arrangement and the TiO,

formed collection in an aqueous suspension of pigment.

The solids component was filtered off and washed, dried and ground.

The TiO, pigment obtained had the following properties:

Brightening power according to DIN 62 193 860 Reynolds number 1950 Mostfrequent volume diameter 0.231 p. --g (distribution width) 1.37

The pigment particle fraction larger than 0.25 p. amounted to 2 percentand the proportions of particles smaller than 0.18 n amounted toapproximately 3 percent. These figures were obtained by counting fromphotographs taken with an electron microscope. I

The test was stopped after 3 days. No disturbances in the production ofthe pigment were recorded over this period. The pigment properties werehighly constant. The large deflection chamber was examined after thetest. There were no signs of any appreciable deposits. The apparatus hadremained completely free fromobstruction during the entire test, norwere any appreciable pressure differences noticed during the test.

By way of comparison, another test was carried out, corresponding in itsdetails to. the test described above, the only difference being that onthis occasion the two changes in direction were avoided. The cold gaswas introduced at 6, as shown in the drawing, and after a certaindistance (without any change in direction), the pigment was completelycooled and deposited.

The product obtained had the following properties:

Brightening power according to DIN 62 193 790 Reynolds number l725 Mostf uent volume diameter 0.224 p. -g (distnbution width) 1.58

It will be appreciated that the instant specification and examples areset forth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention What is claimed is:

1. In the process for cooling gas/solids suspensions of the kind formedduring the reaction of metal halides with gases containing oxygenwherein the gas/solids suspension is mixed with cold gas and thentreated for separation of solids, the improvement which comprisesabruptly changing the direction of flow of the mixture of cold gas andgas/solids suspension, reducing its rate of flow, abruptly changing itsdirection of flow a second time, and increasing its rate of flow,whereby cooling is effected quickly and uniformly.

2. A process as claimed in claim 1, wherein the cooled gas ultimatelyseparated from the solids is used as the cold gas.

3. A process as claimed in claim 1, wherein the gas/solids streaminitially flows at a rate of about 10 to meters per second, its rate offlow is reduced by a factor of about 2 to 20 and its rate of flow isthereafter increased again.

4. A process as claimed in claim 1, wherein the gas/solids streaminitially flows at a rate of about 10 to 100 meters per second, its rateof flow is reduced by a factor of about 2 to 20, and its rate of flow isthereafter increased to about 30 to 200 percent of its initial rate.

5. A process as claimed in claim 1, wherein the temperature of thegas/solids suspension on leaving the zone of low flow rate is in therange from about 500 t 800C.

6. A process as claimed in claim 1, wherein the cold gas is dischargedinto the flowing gas/solids suspension substantially radially so as toeffect rapid cooling.

7. A process as claimed in claim 1, wherein the cold gas is dischargedannularly about the flowing gas/solids suspension so as to effectrelatively slow cooling.

8. A process as claimed in claim 1, wherein the gas/solids suspensioncomprises chlorine, oxygen and optionally carbon dioxide as the gas andthe oxide of at least one of titanium, silicon, zirconium, chromium,aluminium, iron and zinc as the solids.

9. A process as claimed in claim 8, wherein the cooled gas ultimatelyseparated from the solidsis used as the cold gas, the gas/solids streaminitially flows at a rate of about 10 to 100 meters per second, its rateof flow is reduced by a factor of about 2 to 20 and its temperature isreduced to about 500 to 800C, and its rate of flow is thereafterincreased to about 30 to 200 percent of its initial rate, any solidsdeposited in the zone of low flow rate being continuously scraped away.

l i i

2. A process as claimed in claim 1, wherein the cooled gas ultimatelyseparated from the solids is used as the cold gas.
 3. A process asclaimed in claim 1, wherein the gas/solids stream initially flows at arate of about 10 to 100 meters per second, its rate of flow is reducedby a factor of about 2 to 20 and its rate of flow is thereafterincreased again.
 4. A process as claimed in claim 1, wherein thegas/solids stream initially flows at a rate of about 10 to 100 metersper second, its rate of flow is reduced by a factor of about 2 to 20,and its rate of flow is thereafter increased to about 30 to 200 percentof its initial rate.
 5. A process as claimed in claim 1, wherein thetemperature of the gas/solids suspension on leaving the zone of low flowrate is in the range from about 500* to 800*C.
 6. A process as claimedin claim 1, wherein the cold gas is discharged into the flowinggas/solids suspension substantially radially so as to effect rapidcooling.
 7. A process as claimed in claim 1, wherein the cold gas isdischarged annularly about the flowing gas/solids suspension so as toeffect relatively slow cooling.
 8. A process as claimed in claim 1,wherein the gas/solids suspension comprises chlorine, oxygen andoptionally carbon dioxide as the gas and the oxide of at least one oftitanium, silicon, zirconium, chromium, aluminium, iron and zinc as thesolids.
 9. A process as claimed in claim 8, wherein the cooled gasultimately separated from the solids is used as the cold gas, thegas/solids Stream initially flows at a rate of about 10 to 100 metersper second, its rate of flow is reduced by a factor of about 2 to 20 andits temperature is reduced to about 500* to 800*C., and its rate of flowis thereafter increased to about 30 to 200 percent of its initial rate,any solids deposited in the zone of low flow rate being continuouslyscraped away.